The present invention relates to a warp let-off mechanism of a weaving machine, having a speed change transmission for changing the speed of the warp beam rotation in accordance with warp tension. More specifically, the present invention relates to a device for changing the direction of the warp beam rotation.
In a positive warp let-off mechanism of a known type, there are provided a back roller for sensing warp tension, and a speed change transmission for changing the speed of the warp beam rotation in accordance with the warp tension. The warp yarns are released from the warp beam, and introduced to the heald through the back roller. The back roller is acted upon by the warp tension, and moves in accordance with the warp tension. The speed change transmission is connected with the back roller. The speed change transmission increases the warp letting off rate if the warp tension increases beyond an allowable range, and decreases the warp letting off rate if the warp tension decreases below the allowable range. In this way, this warp let-off mechanism automatically controls the warp tension within the allowable range.
Japanese Utility Model examined publication No. Sho 51-17332 discloses one type of such a speed change transmission. In this speed change transmission, there are provided a plurality of eccentrics mounted on an input shaft, and a plurality of control arms swingable on a common shaft whose position is changed in accordance with the warp tension. The eccentrics are connected with the control arms, individually, in such a manner that the eccentrics converts the rotation of the input shaft into a reciprocating motion, and the stroke of the reciprocating motion is varied in accordance with the position of the common shaft determined by the warp tension. This reciprocating motion is transmitted to an output shaft, and converted to a rotation of the output shaft by a freewheel mechanism (a one-way clutch). Thus, the warp beam is driven by the output shaft rotation while the ratio between the input speed and the output speed is controlled in accordance with the position of the common shaft.
In this speed change transmission, the output shaft rotation is always fixed in the forward direction irrespective of whether the direction of the weaving machine movement is forward or reverse, because this speed change transmission utilizes the reciprocating motion. The warp beam is driven in the forward direction both when the weaving machine is driven in the forward direction and when the weaving machine is driven in the reverse direction.
When the weaving machine is stopped and then moved in the reverse direction in order to repair a mispick or other malfunction, this speed change transmission drives the warp beam in the forward direction whereas a surface roller on the fabric take-up side is rotated in the reverse direction. Therefore, the warp yarns become very slack, and the back roller moves so that the ratio of the input and output speeds changes extremely. Therefore, very troublesome and time-consuming preparations for readjusting the warp tension and other conditions are required for restarting the weaving operation every time the weaving machine is stopped and moved in the reverse direction.
In one type of such a speed change transmission, there is further provided a shift mechanism which can change the direction of the output shaft rotation from the forward direction to the reverse direction and vice versa. If, however, the shift mechanism is operated incorrectly, there arises a dagerous condition in which the weaving machine is driven in the forward direction whereas the warp beam is driven in the reverse direction. In this condition, the warp tension rises to an abnormal level, so that there is a fear of breakage of many warp threads, and a serious defect of a woven fabric.